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Non-Controlling Interests - Subsidiaries and Operations with Non-Controlling Interests (Details) - MW |  | 1 Months Ended | 3 Months Ended | 4 Months Ended | 6 Months Ended | 11 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Oct. 19, 2018 | Dec. 31, 2018 | Jul. 30, 2018 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Nov. 29, 2018 | Dec. 31, 2020 | Jun. 21, 2018 | Dec. 31, 2020 | Dec. 31, 2019
TransAlta Cogeneration, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests |  |  |  |  |  |  |  |  |  |  |  |  | 49.99% | 49.99%
TransAlta Renewables Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests |  |  |  |  |  |  |  |  |  |  |  |  | 39.90% | 39.60%
Proportion of equity participation in subsidiary |  | 60.90% | 61.10% | 60.20% | 60.30% | 60.40% | 60.50% | 60.60% | 60.80% | 61.00% | 60.10% | 64.00% |  |
TransAlta Renewables Inc. | Kent Hills wind farm |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests |  |  |  |  |  |  |  |  |  |  |  |  | 17.00% |
Capacity of facility (in megawatts) |  |  |  |  |  |  |  |  |  |  | 167 |  | 167 |
Kent Hills 3 Wind Project |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in contractual power capacity (in megawatts) | 167 |  |  |  |  |  |  |  |  |  |  |  |  |

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- Definition The proportion of ownership interests in a subsidiary held by non-controlling interests. [Refer: Subsidiaries [member]; Non-controlling interests] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2019-01-01 -Paragraph 12 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2019-en-r&anchor=para_12_c&doctype=Standard -URIDate 2019-03-27 + Details
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